The copper-chlorine (Cu—Cl) cycle was identified as one of the promising lower temperature cycles to produce hydrogen (Lewis et al., 2003; Serban et al., 2004). The Cu—Cl cycle includes three chemical reactions to decompose water into hydrogen and oxygen. Two of the chemical reactions are thermal and one is an electrochemical reaction. The three reaction steps of the Cu—Cl cycle (FIG. 1) are (Marin, 2012; Abdulrahman, 2016a; Abdulrahman, 2016b):2CuCl(a)+2HCl(g)→2CuCl2(a)+H2(g)100° C.  step(1)2CuCl2(s)+H2O(g)Cu2OCl2(s)+2HCl(g)375° C.  step (2)Cu2OCl2(s)→2CuCl(l)+½O2(g)530° C.  step (3)where a, s, l and g denote aqueous, solid, liquid and gas, respectively. These three reaction steps of the Cu—Cl cycle are shown in FIG. 1.
In the oxygen production step of the Cu—Cl cycle (i.e. step 3), solid copper oxychloride (Cu2OCl2) is decomposed thermally into oxygen gas (O2) and molten cuprous chloride (CuCl). The solid Cu2OCl2 is fed to an oxygen production reactor (i.e. a thermolysis reactor) from the CuCl2 hydrolysis reaction (i.e. step 2) that operates at a temperature range of 350-450° C. The materials leaving the thermolysis reactor are oxygen gas (which is evolved over a temperature range of 450 to 530° C.) and molten CuCl. In the thermolysis reactor, the decomposition of Cu2OCl2 to oxygen and molten CuCl is an endothermic reaction requiring a reaction heat of 129.2 kJ/mol and a temperature of 530° C., which is the highest temperature in the Cu—Cl cycle. Thus, heat must be added to increase the temperature of the bulk material inside the thermolysis reactor. The total amount of heat required is the sum of reaction heat and the heat required to raise the reactant temperature from 375° C. (the average temperature of solid particles from the hydrolysis reaction) to 530° C. (Naterer et al. 2008b; Abdulrahman, 2016a).
The design and scale-up (i.e. geometric and production scaling) of the thermolysis reactor must be studied from different perspectives, such as; kinetics, hydrodynamics, mass and heat transfer. In order to scale up the thermolysis reactor from the perspectives of the hydrodynamics and heat transfer, it is necessary to conduct some experiments to describe the hydrodynamic and thermal behaviors. However, experimentally, there are some challenges in using the actual products of the thermolysis reactor (i.e. O2 and CuCl) at the operating conditions of the thermolysis reactor. The challenges are: 1) the cuprous chloride (CuCl) has a high melting temperature of 430° C., 2) the color of CuCl after melting is a non-transparent dark grey, which makes it difficult to see oxygen bubbles inside it, 3) the cuprous chloride molten salt is very corrosive, 4) the oxygen gas is a strong oxidizing agent which will quickly combust materials, and 5) it is a high temperature process.